LANDING GEAR SOLENOID...
(100100)
From: arbeau@napanet.net (Denis M Arbeau)
My mechanic recently replaced the landing gear solenoid on another Swift
when the owner reported that the gear wouldn't work and troubleshooting
confirmed it was a bad solenoid. The owner came up with another (automotive)
solenoid and they installed it. Ops check good. Now, however, after some
use THIS solenoid has also failed. John took the solenoid apart and said
it is rather cheaply made. He was wondering if you have advice (ie. part
number and/or application) for a GOOD solenoid that they might buy. Let
me know. Thanks! Denis

Denis,
Aircraft Spruce has p/n 111-226 (continuous) and p/n 22735 (intermittent)
relays. Either will work, although the intermittent (starter) relay should
be better even if it does have a plastic case. Recently I needed a relay
right now so I went to a local auto parts store and bought one, it was
about twice the price! Aircraft Spruce gets about $15.00 -- Jim

RELAY FOR LANDING GEAR...(010201)From: John Tuuri <JTuuri@aol.com>
Monty-- I am installing the Merlyn STC for the hydraulic powerpack and
can not find my copy of your comments relating to the replacement of the
relay that were in one of the GTS Updates recently.. Could you suggest
a replacement? Thanks....Jon Tuuri

John,
Get a 111-226 ($16.95) in Aircraft Spruce. Contrary to what I may have
said at one time you want a continuous duty solenoid. -- Jim

INTERMITTENTLY CONTINUOUS...(010401)
Subj: Solenoids?
From: Graham Gitlin <gngitlin@ucdavis.edu>
Monty, I have a quick question for you. I currently have Swift N78230,
Charlie's first Swift, which has a Merlyn hydraulic motor. I have used
an intermittent duty solenoid for the motor as previously recommended,
but now understand that you are recommending a continuous duty solenoid.
Could you please explain why the change?, and what are the significant
differences between the intermittent duty and continuous duty solenoids?
Thanks in advance.

Graham,
The intermittent duty relay will get hot when engaged for a period of
time. The continuous duty relay is wired so there won't be a buildup of
heat even when engaged for many hours. (maybe a REAL electric wizard will
jump in and explain this better!) The little green light circuit keeps
a small load in the gear circuit continuously. I have always used continuous
duty relays, but when I got thinking about it, I thought, why not use
a starter type relay? I had forgotten about the continuous load. -- Jim

SPEAKING OF SOLENOIDS:
GOOD INFO FROM SOMEONE WHO KNOWS...(010401)Subj: Landing gear motor fun
From: Ronald Williamson <rwwilliamson@earthlink.net>
Monty, Here's my analysis of the motor/solenoid mystery...
First the solenoid: The momentary rated solenoid is just fine for the
gear motor relay replacement. I changed my original bakelite one when
I did the first rebuild of 40K back in 1975 and put in a starter relay.
It's still working fine. The difference between a continuous and intermittent
is the enthusiasm with which they close. The continuous rated has a higher
resistance coil which draws fewer amps when energized. It can thus stay
energized and not make too much heat todamage itself. However, it closes
and opens with less force because the reduced coil current also means
less force to close the contacts. Once the contacts are closed, they can
pass the same amount of current as the intermittent type. The intermittent
contacts are made to break large starter motor currents and therefore
has a lower resistance coil which makes more force to "snap"
the main contacts open and closed. However, the higher coil current gets
the solenoid hotter and intermittent types can self destruct if left on
continuously. The gear motor is a small load to make and break as compared
to a starter motor, so either type solenoid will work just fine.

Now for the fun. The Swift
landing gear circuitry is detailed in Figure 32 on Page 77 of the old
red "Operator's Handbook". The same circuit has been copied
into the oft-mentioned manual produced by Mr. Commings. So, assuming Jon's
Swift is wired "stock", then it can be used. The green light
is NOT part of the solenoid circuit. The green light is only energized
when EITHER gear is in the down position and the corresponding micro switch
is closed. Thus, the circuit can be split and independent greens for each
gear can be wired without affecting the operation of the gear. I think
Dick Collins has that circuit detailed out somewhere. More importantly,
the red gear light is not a gear UP indicator. It only indicates the gear
is NOT DOWN (in 40K the red light is labeled "UNSAFE"). That
is, if either down microswitch moves enough to "click" then
the red light will be turned on. With either the stock or split green
wiring, a red AND a green is a normal indication when the gear is transitioning.
Since one gear always goes first, it will turn on the red light while
the remaining gear is still green. When both gear move off the bottom
microswitch, then only a red indication is seen. When the gear hits the
top microswitch, the current to the coil is broken and the hydraulic motor
shuts off. Thus, gear UP is only indicated by the yellow hydraulic pump
light turning off.

How does the solenoid get
energized? The center post of the gear switch on the backside of the operating
handle is connected to the solenoid coil. The top post of the gear switch
is connected to the red gear lamp through the resistor which limits the
brightness to extend the bulb life - and make it less obtrusive during
night ops) and to wire #26 on the diagram. The bottom post of the switch
is connected to wire #27. The astute student will note that Up and Down
labels on the switch in Figure 32 are reversed. That is, closing the top
contact causes the gear to go down and vice versa. When the Swift is on
the ground and the gear selector is in the down position, the red light
circuit is connected to the coil of the gear solenoid. If either down
microswitch opens, then the red light comes on which also powers the solenoid
coil and runs the pump to force the gear against the down stop which then
opens the down microswitch to turn off the solenoid and stop the motor.
Conversely, when the gear switch is set to Up (only after suitable altitude
and airspeed), then the solenoid is energized because that side of the
circuit is energized when either of the Up microswitches is closed. When
BOTH gear hit the top switch, then the coil current is interrupted. If
either gear falls out of the well during flight due to misadjustment of
the emergency cable or who knows what, then the Up microswitch closes,
energizing the solenoid and running the motor until the gear is against
the Up stop again. 40K used to do that at 20 minute intervals until I
got the extension cable adjusted properly.

So, after all the above blather,
what's going on with Jon's Swift? The hydraulic pump is clearly running
because the flaps are operating. Figure 34 shows how that is possible,
since the flap microswitches in the belly are used to switch the hydraulic
motor current directly!!! Not a good idea in my opinion, but it's worked
for many years. Out of a need for purity, I used a diode across the back
of my flap switch to isolate the gear/flap circuits and 40K now uses the
solenoid to start the motor for both gear and flaps. But, I digress. What
this means is that the gear and flap circuits are essentially independent.
If the motor runs, we know that the 30A breaker on the instrument panel
is good and that the wiring to the yellow light and to the motor is correct.
If the solenoid doesn't close regardless of the gear switch position,
then it is possible that the solenoid isn't wired correctly. The solenoid
coil has 2 posts. One post is connected to wire #24 which leads back to
the center post of the gear selector switch. Continuity can be checked
to verify that connection. Open the circuit breakers and turn the master
off before checking with an ohmmeter. The other coil post connects to
ground to complete the circuit when the gear switch applies the 12V. If
the coil isn't grounded, the motor will never run regardless of the gear
handle position. As far as the red/green indication, I'd guess a sticky
microswitch in the wheel well. Since the lights are powered from the 5A
circuit breaker, we know the breaker is working or we'd see no lights.

In summary:

1. Verify continuity between
the solenoid coil and the center of the gear handle toggle switch behind
the panel.

2. Verify the second coil
post on the solenoid is solidly connected to ground. The mounting screw
on the firewall is typically used.

3. Jack the Swift (with suitable
precautions about sandbags on the horizontal) and verify the microswitches
are free and operating.

4. With the gear down and
the gear circuit breaker (5A) on, should have only a green light. Check
the voltage at the bottom terminal of the gear selector toggle switch
and verify it has 12V.

5. If all checks ok, then
gear should retract normally.

Ron

COUNT THE TERMINALS ON
THE SOLENOID BEFORE YOU BUY...(010401)
Subj: Mystery solved
From: Ron Williamson <Ronald.W.Williamson@aero.org>
Monty,
Turns out that Jon had purchased a "Master Switch" solenoid
which has only 3 terminals. In that configuration, the coil power is internally
connected to the BAT terminal and the small coil post is grounded to activate
the solenoid. So, when he connected the small post to the gear switch,
it provided +12V back to the selector switch. With the gear in the "Down"
position, that illuminates the red light! The green is illuminated correctly
because it's powered off the other contact of the down microswitches.
Of course the solenoid coil will never energize because the gear switch
also provides +12V so the coil sees a net of zero volts. Jon is going
to get the isolated coil version (4 terminals), hook up the ground per
the original configuration and he'll be good to go. I always enjoy it
when there's a sensible explanation for an impossible situation. -- Ron

p.s. Please pass this info
along to Jon if you can. This part will work for the pump motor. Grainger
stocks this part so it should be easy to get. Around $22 list, but nobody
pays list at Grainger.
Grainger Item No: 6C028
Mfg. Model No: 70-111224-5
Manufacturer: ESSEX WHITE RODGERS